Obesity, which currently affects 25 percent of children, is one of the main causes of pediatric hypertension, and remains a risk factor for non- insulin-dependent diabetes, coronary heart disease and early death when it persists into adulthood. Unfortunately the incidence of obesity in children is increasing despite the fact that our society has become more health and fitness conscious. The aims of this project are: 1. To characterize the pre-obese state with regard to energy expenditure, physical activity and body composition. 2. To identify environmental and phenotypic markers for the development of human obesity. 3. To derive estimates of energy requirements in children based on measurements of energy expenditure, rather than on energy intake data. The project consists of a longitudinal study in children commending at age 4-6 and continuing for a six year period. The following outcome variables are measured in the children; total daily energy expenditure using doubly labeled water, resting energy expenditure using indirect calorimetry, energy expenditure of physical activity, dietary intake, total body water, body fat using DXA and bioelectrical impedance, fat distribution using anthropometrics, and pubertal development using Tanner staging. To date seven children from Vermont have completed the year six protocol. In 1998 an additional seven children are scheduled to complete the protocol.